JPH0795082B2 - Power supply voltage monitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a power supply voltage monitor for confirming or monitoring whether or not the voltage of a DC or AC power supply circuit such as a tape deck is appropriate.

[Prior Art] A simple voltage monitor in which a light emitting diode 5 is connected between power supply terminals 1 and 2 via a resistor 3 and a zener diode 4 as shown in FIG. 9 is already known. In this monitor, a zener diode is used. When a voltage equal to or higher than the Zener voltage of 4 is applied between the pair of terminals 1 and 2, the light emitting diode 5 lights up.

[Problems to be Solved by the Invention] However, the monitor of FIG. 9 can determine whether the power supply voltage is high or low, and cannot know whether or not the power supply voltage is within a predetermined range.

Therefore, an object of the present invention is to provide a power supply voltage monitor capable of knowing whether or not the power supply voltage is within a predetermined range despite having a simple circuit configuration.

[Means for Solving the Problems] The present invention for achieving the above-mentioned object is provided between first and second terminals for connecting to a power supply circuit, and between the first terminal and the second terminal. A light emitting element connected to the first terminal, the first zener diode connected between the first terminal and the light emitting element, and the first zener diode between the first terminal and the light emitting element. First connected in series to
Parallel to the series circuit of the resistor, the second resistor connected between the light emitting element and the second terminal, the light emitting element, the first Zener diode, and the first resistor. A second Zener diode connected in parallel with a series circuit of the light emitting element and the second resistor, the third Zener diode being connected in parallel to the series circuit of the light emitting element and the second resistor, and the first terminal and the first Zener diode. When the voltage between the second terminal and the second terminal is lower than the first value, the first, second and third Zener diodes are non-conducting, the light emitting element is turned off, and the first terminal and the first terminal When the voltage between the first terminal and the second terminal is within the range from the first value to a second value higher than the first value, the first Zener diode conducts and the light emitting element lights up, The voltage between the first terminal and the second terminal is greater than the second value. When the first, second and third Zener diodes are turned on and the light emitting element is turned off, the Zener voltages and the first and second resistors of the first, second and third Zener diodes are turned off. And a zener voltage of the third zener diode is set to be slightly higher than a forward voltage of the light emitting diode during light emission.

Further, it is preferable to connect another light emitting diode in series to the second Zener diode in the power supply voltage monitor of the above invention.

[Operation] In the power supply voltage monitor according to claim 1, if the voltage between the first and second terminals is gradually increased, first, the first Zener diode is turned on to turn on the light emitting element. ,
Next, the third Zener diode becomes conductive and a substantially constant voltage is applied to the light emitting element. When the power supply voltage is further increased, the second Zener diode becomes conductive and the connection point between the light emitting diode and the second resistor is reached. Potential rises, the voltage across the light emitting element decreases, it becomes impossible to maintain the light emission of the light emitting element, and the light is turned off. Therefore, the light emitting diode can be turned on only within the proper voltage range. The third Zener diode has a function of limiting an increase in current of the light emitting element, and also has a function of turning off the light emitting element when the second Zener diode is turned on.

In the invention of claim 2, when the voltage is lower than the proper voltage, 2
Two light emitting elements are turned off, one light emitting element is turned on almost corresponding to the appropriate voltage range, and one light emitting element is turned off when higher than the upper limit value of the appropriate voltage range or in the vicinity thereof,
The other light emitting element lights up.

[First Embodiment] The power supply voltage monitor of the first embodiment according to the present invention comprises a first and second terminals 11 and 12, an LED, that is, a light emitting diode 13.
And the first, second and third Zener diodes 14, 15,
16 and first, second and third resistors 17, 18, and 19. The first resistor 17, the first Zener diode 14, the light emitting diode 13, and the second resistor 18 are connected in series with each other and between the first and second terminals 11 and 12. The second Zener diode 15 is connected between the first terminal 11 and the cathode of the light emitting diode 13 via the third resistor 19. The third Zener diode 16 is connected between the anode of the light emitting diode 13 and the second terminal 12.

Now, assuming that the lower limit voltage of the proper voltage range is V1, the upper limit voltage is V3, and the zener voltages of the first and second zener diodes 14 and 15 are Vz1 and Vz2, Vz1 is set to be somewhat lower than V1. Vz2 is set somewhat lower than V3, and Vz1 <Vz2. As a result, the light emitting diode 13 is turned on only when an appropriate voltage in the range of V1 to V3 is applied between the first and second terminals 11 and 12.

The operation will be described in more detail with reference to FIG. Power supply voltage V
Becomes V1, the first zener diode 14 becomes conductive and the light emitting diode 13 emits light. Light emitting diode
Letting VF be the on-state voltage of VF, the values of the first and second resistors 17 and 18 be R1 and R2, and the current flowing therethrough be I1, the following equation holds.

V = I1R1 + Vz1 + VF + I1R2 Therefore, in order to light the light emitting diode 13 at a voltage of V1 or higher, Vz1 + VF must be set smaller than V1.

The Zener voltage Vz3 of the third Zener diode 16 is set to be somewhat higher than the forward voltage VF of the light emitting diode 13. Voltage VF of light emitting diode 13 and voltage I1R of resistor 18
When the sum of 2 and 3 becomes higher than the Zener voltage Vz3 of the third Zener diode 16, the third Zener diode 16 becomes conductive and the increase in the current flowing through the light emitting diode 13 is suppressed.

When the power supply voltage V becomes V2, which is slightly lower than V3, the second Zener diode 15 is turned on, and the current flowing there
I2 becomes large. As a result, the current flowing through the second resistor 18 also increases, and the voltage Vd between both terminals Vd = R2 (I1 + I2) also increases, so that the current I1 of the light emitting diode 13 decreases and the light emission amount of the light emitting diode 13 decreases. . When the power supply voltage becomes V3 and the inter-terminal voltage Vd of the second resistor 18 becomes higher than Vz3-VF, the voltage applied to the light emitting diode 13 becomes lower than this rising voltage, and the light is turned off. Even if the power supply voltage becomes higher, the light-emitting diode 13 is kept turned off.

[Second Embodiment] Next, a power supply voltage monitor according to a second embodiment of the present invention shown in FIG. 3 will be described. However, in FIG. 3 and FIGS. 5 and 6 described later, the reference numerals 11 to 19 are substantially the same as those shown in FIG.
The description is omitted. In the power supply voltage monitor of FIG. 3, the first Zener diode 14 is connected in series with the first
In addition to the light emitting element 13 of, the second light emitting diode 20 is connected in series to the second Zener diode 15, the first light emitting diode 13 is a green light emitting diode (green LED), and the second light emitting diode 20 is red. It is said to be a light emitting diode (red LED).

In this case, as is clear from FIG. 3, the current of the first light emitting diode 13, that is, the green LED, flows as in FIG.
On the other hand, the current of the second light emitting diode 20 or the red LED is the second
The zener diode 15 starts to flow from the voltage V2 at which it turns on, and when the voltage reaches V3, the second light emitting diode 20 is completely lit. Therefore, the first and second light emitting diodes 13,
It is known that the power supply voltage V is lower than the desired range because both of them are turned off, and the first light emitting diode 13 is turned off and the second light emitting diode 20 is turned on so that the power supply voltage V is within the desired range. You can know that it is higher than.

Further, in this embodiment, since the two LEDs 13 and 20 have different emission colors, it is possible to easily determine whether the power supply voltage is excessive or insufficient.

[Third Embodiment] In the power supply voltage monitor of the third embodiment shown in FIG. 5, a resistor 21 is further added in addition to the second light emitting diode 20. When the resistor 21 is connected in parallel with the second light emitting diode 20, the voltage drop I3R4 caused by the current I3 flowing through the resistor 21 and the value R4 of the resistor 21 becomes the forward voltage VF when the second light emitting diode 20 is on. Until then, the second light emitting diode 20 does not light up. Therefore, by adjusting the value R4 of the resistor 21, the second light emitting diode 20, that is, the red LED can be turned on at the power supply voltage V3 as shown in FIG. The first light emitting element 13 is turned on as in the case of FIGS. According to this FIG. 5, two light emitting diodes
The simultaneous lighting areas of 13 and 20 can be excluded, and it becomes possible to clearly identify the overvoltage state.

[Modifications] The present invention is not limited to the above-described embodiments, and the following modifications are possible, for example.

(1) As shown in FIG. 7, a rectifier diode 22 may be connected in series to the terminal 11 to monitor the AC power supply voltage. The rectifier diode 22 is the Zener diode 14,
It also functions to prevent backflow of the light emitting diodes 15, 16 and the light emitting diodes 13, 20. This diode 22 can also be connected to the circuits of FIGS. 1 and 5.

(2) The rectifying / smoothing circuit consisting of the rectifier 23 and the capacitor 24 shown in FIG. 8 is connected to the terminal 11 shown in FIG. 1, 3, or 5.
It may be connected to 12 and used as an AC power supply voltage monitor.

(3) A negative voltage monitor with respect to the ground can be configured.

[Effects of the Invention] As described above, according to the power supply voltage monitor according to claim 1, since the light emitting element is turned on within a desired voltage range and is turned off at both a lower voltage and a higher voltage, It is possible to know whether or not the power supply voltage is within the desired range by the light emitting element. Therefore, a simple power supply voltage monitor can be provided.

In the power supply voltage monitor according to the second aspect, since the second light emitting element is turned on by utilizing a part of the control circuit of the first light emitting element, voltage monitoring by the two light emitting elements is achieved by a simple circuit. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a power supply voltage monitor according to a first embodiment of the present invention, FIG. 2 is a view showing a relation between a power supply voltage of the circuit of FIG. 1 and a current of a light emitting diode, and FIG. FIG. 4 is a circuit diagram showing a power source voltage monitor of a second embodiment of the invention, FIG. 4 is a diagram showing a relationship between the power source voltage of the circuit of FIG. 3 and the current of each light emitting diode, and FIG. 6 is a circuit diagram showing a power supply voltage monitor of the embodiment of FIG. 6, FIG. 6 is a diagram showing a relationship between the power supply voltage of the circuit of FIG. 5 and a current of each light emitting diode, and FIG. 7 is a circuit showing a power supply voltage monitor of a modified example. FIG. 8 is a diagram showing a rectifying / smoothing circuit portion of a power supply voltage monitor of a modified example, and FIG. 9 is a circuit diagram showing a conventional power supply voltage monitor. 11 ... First terminal, 12 ... Second terminal, 13 ... Light emitting diode, 14 ... First zener diode, 15 ... Second
Zener diode, 16 ... Third Zener diode, 17 ... First resistance, 18 ... Second resistance, 19 ... Third
Resistance, 20 …… second light emitting diode, 21 …… resistor.

Claims (2)

[Claims] 1. A first and a second terminal for connecting to a power supply circuit, a light emitting element connected between the first terminal and the second terminal, the first terminal and the First connected to the light emitting element
Zener diode, a first resistor connected in series to the first zener diode between the first terminal and the light emitting element, and connected between the light emitting element and the second terminal The second done
Of the resistor, a second Zener diode connected in parallel to a series circuit of the light emitting element, the first Zener diode, and the first resistor, and the light emitting element and the second resistor A third Zener diode connected in parallel to the series circuit, wherein when the voltage between the first terminal and the second terminal is lower than a first value, 2 and the 3rd Zener diode are non-conducting, the said light emitting element is light-extinguished, and the voltage between the said 1st terminal and the said 2nd terminal is more than this 1st value from this 1st value. The first Zener diode conducts to turn on the light emitting element when the voltage is within the range up to the second value, and the voltage between the first terminal and the second terminal is the second value. Higher than, the first, second and third Zener diodes conduct. The first as the light emitting element is turned off, the second and third Zener diodes Zener voltage and the first and second
The resistance value of the resistor is set, and the Zener voltage of the third Zener diode is set to be somewhat higher than the forward voltage of the light emitting diode during light emission. 2. The power supply voltage monitor according to claim 1, further comprising another light emitting diode connected in series with the second Zener diode.